The present invention relates to a novel ink composition which results in excellent image quality as well as high image fastness and an image forming method, and in more detail to an ink composition which can be employed in an ink jet recording method and an image forming method which is capable to accomplishing ink jet recording.
An ink jet recording method makes it possible to record extremely fine images employing a relatively simple apparatus, and has been increasingly developed in various fields. In broad fields, produced have been printers which utilize ink jet recording systems. Further, a wide variety of ink has been developed depending on need.
Water based ink jet recording compositions are commonly employed for ink jet recording. The water based ink jet recording compositions employed for ink jet recording are mainly divided into dye based ink and pigment based ink.
The dye based ink is highly valued on the market due to its vivid color reproduction as well as its excellent storage stability. On the other hand, it does not sufficiently meet requirements for image retention quality (such as light fastness, minimum bleeding, and the like).
The pigment based ink exhibits higher image retention compared to the dye based ink, but it necessitates a dispersion process for its production. The stability of the resultant dispersion is limited. Therefore, when employing ink jet recording, problems occur such as disadvantages for cost reduction, clogging during use over an extended period of time, and the like. Further, the resultant image quality (such as color reproduction, glossiness, bronzing, and the like) is inferior to dyes.
Under such current situation, demanded have been novel colorants which exhibit the excellent properties of dyes (such as image quality and ink storage stability) and the image retention quality of pigments (such as light fastness, minimum bleeding, and the like).
In recent years, developed has been technology in which specified pigments are subjected to chemical modification so that they become soluble in organic solvents. For example, Japanese Patent Publication Open to Public Inspection No. 7-150068 discloses organic solvent-soluble compounds in which nitrogen atom(s) of pigments such as quinacridone, indigo, and the like, are subjected to chemical modification employing a specified oxycarbonyl group, and further discloses that when the resulting modified compound is subjected to thermal treatment, the original pigment is regenerated (latent pigment technology).
Further, Japanese Patent Publication Open to Public Inspection Nos. 11-246809 and 11-293166 disclose technology in which said latent technology is applied to ink jet recording. However, compounds, which are obtained by substituting disclosed pigments, are only soluble in organic solvents. Thus when ink is prepared, water-insoluble organic solvents are required.
Employed as water-insoluble organic solvents, which are employed to prepare said ink, are low-boiling point and high-boiling point water-insoluble organic solvents. Said low-boiling point water-insoluble organic solvents are not preferred because during printing as well as the drying process, organic solvents volatize to result in adverse effects to humans as well as to the environment. Further, the volatilization of said water-insoluble organic solvents on the printing head results in frequent clogging of the orifice of said head. Still further, when said high-boiling point water-insoluble organic solvents are employed, the drying properties of images are degraded and a large amount of solvent remains. Specifically, when special glossy paper sheets, which are capable of producing high quality, are used, drying properties are further degraded. As a result, when the printed paper sheet is placed on another, parts of the image may be transferred to the reverse surface.
It is a first object of the present invention to provide an ink composition which exhibits storage stability of ink for an extended period of time and results in high image quality as well as sufficient image retention. It is a second object of the present invention to provide a method which forms images exhibiting high image quality as well as sufficient image retention, employing a novel water based ink composition.
The aforementioned objects of the present invention are achieved by the embodiments described below.
(1) A water based ink composition characterized in that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is dissolved in a water based solvent.
(2) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (1) described below: 
wherein R1 represents an alkyl group or an aryl group which may have a substituent, R2 represents a phenyl group which may have a substituent, and R3 represents a phenyl group which may have a substituent. However, at least one of R1, R2, and R3 is a group represented by General Formulas (2) or (3): 
In General Formulas (2) and (3), R4 represents a substituent having a water solubilizing group, R5 represents a substituent, and m2 represent 0 to 3. R6 and R7 each represent a substituent having a water solubilizing group, R8 represents a substituent, and m3 represents 0 to 3.
(3) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (4) described below: 
wherein R9 represents a phenyl group which may have a substituent, R10 represents a hydroxyl group, or an amino group, an acylamino group or a carbamoyl group which may have a substituent, and m4 represents 0 to 7. However, at least one substituent of R9 or R10 is a group represented by General Formula (2) or General Formula (3), or a group R9 or R10 mentioned above which is substituted by the group represented by General Formula (2) or (3). 
In General Formulas (2) and (3), each of R4, R6 and R7 represents a substituent having a water solubilizing group, each of R5 and R8 represents a substituent, and m2 represents 0 to 3.
(4) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (5) described below: 
wherein R1l and R12 each represent a substituent having a water solubilizing group, R13 and R14 each represent a substituent, and n5 and m5 each represent 0 to 4.
(5) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (6) described below: 
wherein R15, R16, R17, R18, and R19 each represent a hydrogen atom or a substituent having a water solubilizing group. However, at least two of R15, R16, R17, R18, or R19 are substituents having a water solubilizing group.
(6) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (7) described below: 
wherein R20 and R21 each represent a substituent having a water solubilizing group, R22, R23, and R24 each represent a substituent, and m7, l7, and n7 each represent 0 to 4.
(7) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (8) described below: 
wherein R25 and R26 each represent a substituent having a water solubilizing group, R27, and R28 each represent a substituent, and m8 and n8 each represent 0 to 4.
(8) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (9) described below: 
wherein R29 and R30 each represent a substituent having a water solubilizing group, and R31 and R32 each represents a hydrogen atom or a substituent.
(9) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (10) described below: 
wherein R33 represents a substituent having a water solubilizing group, and R34 represents a substituent. m10 represents 1 to 8 and n10 represents 0 to 8.
(10) The water based ink composition described in (1) above, characterized in that that a precursor, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is the compound represented by General Formula (11) described below: 
wherein A represents an insoluble pigment residual group; the group in the parenthesis bonds to the nitrogen atom of A; X represents a hydrogen atom or a counter cation; R35 represents a substituent; and l11 represents 0 to 4. Further, when l11 is 2 to 4, a plurality of R35 may be joined together to form a ring. xe2x80x9ckxe2x80x9d represents 1 to 5.
(11) An image forming method characterized in that after carrying out printing on a print medium, employing the water based ink composition described in any of (1) through (10) above, a precursor formed on said print medium, which can be converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means, is converted to an insoluble pigment by at least one means selected from a chemical means, a thermal means, a photodecomposition means, and a radiation means.
(12) The image forming method described in (11) above, characterized in that said chemical means includes one in which an acid is employed as an acting component and a precursor which can be converted to a insoluble pigment is converted to an insoluble pigment by a means in which a means, in which said acid is employed as an acting component, is combined with a thermal means.